Journal of the Royal Society of New Zealand abstracts

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Galaxias fossils from Miocene lake deposits, Otago, New Zealand: the earliest records of the Southern Hemisphere family Galaxiidae (Teleostei)

D. E. Lee¹, R. M. McDowall² and J. K. Lindqvist¹

¹Department of Geology, University of Otago, PO Box 56, Dunedin 9054, New Zealand. daphne.lee@stonebow.otago.ac.nz

²National Institute of Water and Atmospheric Research, PO Box 8602, Christchurch 8440, New Zealand.

Abstract    Galaxiid fishes are commonly assumed to exhibit a Gondwanan distribution, but little fossil evidence has been available to support or refute this assumption until now. Here we report on three species of fossil Galaxias, represented by exquisitely preserved, almost entire skeletons, together with jaw and skull fragments, from several Miocene lacustrine deposits in Otago, South Island, New Zealand. These are the only certain Galaxias fossils, and provide unequivocal evidence that the genus was abundant, and taxonomically and ecologically diverse in the New Zealand region before 23 million years ago. One new species, Galaxias effusus, from an Early Miocene diatomite deposit near Middlemarch is described on the basis of low vertebral count, short caudal peduncle, expansive dorsal, caudal and anal fins, rounded to truncate caudal fin, with 15 principal caudal fin rays. The intact skeletons of G. effusus confirm that they inhabited a deep, stratified maar lake with cool, anoxic bottom water. The maar lake was completely landlocked, from sedimentological evidence, and this species must have been non-migratory. Disarticulated fish jaws and skull fragments from Early Miocene mudstones near Bannockburn are likely to be from a second large species of Galaxias on the basis of dentary, premaxilla and parasphenoid size and morphology. These disarticulated fish remains from a regionally extensive inland lake system indicate decomposition and/or predation in shallow nearshore environments, but we have no evidence yet of migratory behaviour. New specimens of G. kaikorai Whitley from Late Miocene diatomite deposits near Dunedin confirm its morphological similarity to the living G. brevipinnis. The occurrence and diversity of galaxiids in lakes of early and Late Miocene age in southern New Zealand can be explained by either oceanic dispersal across the Southern Hemisphere at any time during the Cenozoic, relict Gondwanan distributions or, most likely, an ancient Gondwanan origin overprinted by Cenozoic dispersal.

Keywords    diatomite; Early Miocene; freshwater fossil fishes; Late Miocene; maar lake

R07002; Received 7 March 2007; accepted 22 July 2007; Online publication date 17 August 2007

Journal of the Royal Society of New Zealand
Volume 37, Number 3, September, 2007, pp 109–130

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